diff --git a/Eigen/src/Core/products/GeneralBlockPanelKernel.h b/Eigen/src/Core/products/GeneralBlockPanelKernel.h
index 0efc07b50..fc3a81c63 100644
--- a/Eigen/src/Core/products/GeneralBlockPanelKernel.h
+++ b/Eigen/src/Core/products/GeneralBlockPanelKernel.h
@@ -1302,7 +1302,13 @@ EIGEN_ALWAYS_INLINE void gebp_micro_panel_impl(GEBPTraits& traits, const DataMap
 
   // Double-accumulation trick for 1pX4 path to break FMA dependency chains
   constexpr bool use_double_accum = (MrPackets == 1 && NrCols == 4);
+#ifdef EIGEN_HAS_CXX17_IFCONSTEXPR
   AccPacketLocal D[use_double_accum ? NrCols : 1];
+#else
+  // Without if constexpr, we must allocate a larger array to satisfy the
+  // compiler that D[n] is always in bounds for the use_double_accum path.
+  AccPacketLocal D[CSize];
+#endif
   EIGEN_IF_CONSTEXPR(use_double_accum) {
     for (int n = 0; n < NrCols; ++n) traits.initAcc(D[n]);
   }
diff --git a/unsupported/Eigen/FFT b/unsupported/Eigen/FFT
index bca5a3ee1..4b7f2397c 100644
--- a/unsupported/Eigen/FFT
+++ b/unsupported/Eigen/FFT
@@ -382,7 +382,7 @@ class FFT {
     defined EIGEN_MKL_DEFAULT
   inline void inv2(Complex* dst, const Complex* src, int n0, int n1) {
     m_impl.inv2(dst, src, n0, n1);
-    if (HasFlag(Unscaled) == false) scale(dst, 1. / (n0 * n1), n0 * n1);
+    if (HasFlag(Unscaled) == false) scale(dst, Scalar(1) / (n0 * n1), n0 * n1);
   }
 #endif